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The disposition of carbamazepine (CBZ) was investigated in the SWV mouse. A 14C-CBZ dose was administered to CBZ pretreated mice, and the distribution of radiolabeled material was determined. Twenty-four hours after the 14C-CBZ dose, 92.5% of the dose was accounted for in urine (56%), in the visera and carcass (22%), in feces (11%), and expired as 14CO2 (2%). CBZ metabolites present in hydrolyzed urine were also identified using a combination of spectroscopic techniques. CBZ, CBZ-10,11-epoxide (CBZE), 2- and 3-hydroxy-CBZ, methylsulfonyl-CBZ, and glucuronides of CBZ and CBZE accounted for 64% of total urinary radioactivity (0-24 hr) in CBZ pretreated mice. Minor metabolites of CBZ included novel cysteine and N-acetylcysteine conjugates of CBZ, as well as a methylsulfonyl conjugate of CBZE not previously reported. The urinary excretion of these thioether conjugates was increased in CBZ/phenobarbital pretreated mice and decreased in CBZ/stiripentol pretreated mice in comparison with CBZ-only treated mice. Preliminary studies of the effects of phenobarbital and stiripentol on the urinary abundance of these metabolites are consistent with the modulation of teratogenicity in the SWV mouse by the same pretreatments. These data suggest the formation of thioether metabolites of CBZ may be related to CBZ teratogenicity in the SWV mouse.

The baculovirus expression vector system was used to overexpress human FMO3 in insect cells for catalytic, structural, and immunochemical studies. Membranes prepared from infected Trichoplusia ni cell suspensions catalyzed NADPH-dependent metabolism of methyl p-tolyl sulfide at rates 20 times faster than those obtained with detergent-solubilized human liver microsomes. Sulfoxidation of the methyl and ethyl p-tolyl sulfides by recombinant human FMO3 proceeded with little stereochemical preference, whereas sulfoxidation of the n-propyl and n-butyl homologs demonstrated increasing selectivity for formation of the (R)-sulfoxide. This chiral fingerprint recapitulated the metabolite profile obtained when detergent-treated human liver microsomes served as the enzyme source. Catalytically active human FMO3 was purified to apparent homogeneity by cholate solubilization and sequential column chromatography on Octyl-Sepharose, DEAE-Sepharose, and hydroxyapatite. Purified FMO3 exhibited the same electrophoretic mobility as native microsomal enzyme, and immunoquantitation showed that this isoform represents approximately 0.5% of human liver microsomal protein. Therefore, FMO3 is quantitatively a major human liver monooxygenase. LC/electrospray-mass spectrometry analysis of purified FMO3 identified >70% of the tryptic peptides, including fragments containing motifs for N-linked glycosylation and O-linked glycosylation. Although insect cells have the capacity for glycan modification, MS analysis of the tryptic peptides demonstrated that these sites were not modified in the purified, recombinant enzyme. Edman degradation of the recombinant product revealed that posttranslational modification of human FMO3 by insect cells was limited to cleavage at the N-terminal methionine, a process seen in vivo with animal orthologs of FMO3. These studies demonstrate the suitability of this eukaryotic system for heterologous expression of human FMOs and future detailed analysis of their substrate specificities.